Study On The Characteristics Of Longmaxi Shale Reservoirs In The Lower Silurian Of Southeastern Sichuan Area

Shale in the Silurian Longmaxi Formation of southeastern Sichuan area is the most Commercial exploitation value of the layer system.Study on reservoir characteristics of the area is important for exploration and development.Through a large number of experiments,including Petrology,organic development characteristics,and physical characteristics and bearing characteristics of four aspects,to study on the black shale.Results show that the dark shale in the Silurian Longmaxi Formation mainly composed of black carbonaceous shale and black shale.Hard tough black shale in the area,and page development,rich in graptolites,Composition consists mainly of quartz(38.2%),clay minerals(36.5%),Followed by carbonate mineral,feldspar,pyrite.Main type of organic matter is sapropel(type I),the mean organic carbon content is 2%,and average overall vitrinite reflectance is 2.6%.Bottom of the porosity is greater than 3%,pore types containing six types,such as micro-cracks,holes,intergranular pores between grains,grain of bore,organic matter and fossil holes.Aperture is mainly concentrated in the 2-10nm range,40%of the total porosity.Shale porosity mainly control by Minerals,organic carbon,and vitrinite reflectance.As rigid particles and the brittle mineral,quartz support the pore,and it is also conducive to the latter fracture.Organic matter content directly affects the proportion of organic hole.Due to the hydrocarbon of the organic matter,organic pore begin to develop.But with the increasing of pressure and temperature,pore will be squashed and be fragmented,aperture becomes smaller and eventually disappear.Effective porosity and gas content and have good positive correlation,when the effective porosity is greater than 2%,the gas content generally is greater than 1.5 cm~3/g;when the effective porosity in 2%~4%,the average gas content is 2.45 cm~3/g,when the effective porosity is greater than 4%,the gas content generally is greater than 4 cm~3/g.The gas contents under the control of Organic carbon,mineral composition and storage conditions,and the organic carbon is the main internal factors,the preservation is the main external factor.The gas content shall be increased with the increase of organic carbon,and shall be increased with the increase of quartz and clay minerals,and shall be decreased with the increase of Carbonate minerals.The gas content in the basin is better than that outside the basin,and the NanChuan area's gas contents is 2.60 cm~3/g,which is mainly composed of free gas,66.8%of the total.The PengShui area's gas contents is 1.31 cm~3/g,which is mainly composed of adsorbed gas,60.6%of the total.The HuaiRen area's gas contents is only 0.49 cm~3/g.